I can't say if Chelsea has improved in their performance or not, it's when the new season starts is when we would know. However, their performance in CWC is impressive and their fate will be tested in the finals when they play against PSG who have destroyed and humiliated top big clubs in various leagues in recent times.
seeing chelsea's performance in the CWC has shown that their performance is quite improved, because to reach the CWC final is not an easy thing. but i agree that to see their real performance we need to wait to see how they perform consistently in heavier and longer competitions, such as the premier league, champions league, or even the fa cup.
as for the match against PSG, i'm not so sure that they can withstand PSG's attack. PSG is currently on fire and their mentality is very good. maybe chelsea's fate will also end up like real madrid yesterday, humiliated in an important match.
Of a truth Chelsea has really improved and I believe next season premier league competition they will perform well and may have the opportunity of lifting the trophy, all they need to do is put more determination and consistency, I know clubs like Arsenal, Liverpool and Manchester City will not just allow them to lift the premier league trophy that easily, for now I can only say that Liverpool and Arsenal are the once that may give them tough time next season, but I can't bet on Chelsea winning the premier league title because I feel Liverpool and Arsenal will have a more better chance than them but like they say football is unpredictable anything can actually happen.
As for the match between Chelsea and PSG on Sunday which is the final in the FIFA club world cup competition, PSG will win Chelsea very well and they will even score them a lot of goals, PSG is more inform than Chelsea so they will win Chelsea, if PSG could win real Madrid and Bayern Munich I don't think Chelsea can stop them.